astro Flashcards
what is one light year
the distance that light travels in one year in a vacuum
9.46x10^15 m
what is parallax
apparent shift in relative position of two objects due to the changing position of the observer
what is the astronomical unit (AU)
the mean distance between the Earth and the sun
is 1.50 x 10^11 m
what is the parsec
A unit of distance that gives a parallax angle of 1 second of an arc (of a degree), using the radius of the Earth’s orbit (1 AU) as the baseline of a right–angled triangle
what is the hipparcos scale
scale which tells you the brightness of a star
what magnitudes are the brightest and dimmest stars
brightest are magnitude 1
dimmest are magnitude 6
what magnitude is used in hipparcos scale
apparent magnitude
what is apparent magnitude
how bright a star appears from earth
why was the apparent magnitude system formalised
our eyes have logarithmic response to light
how many times brighter is magnitude 1 than magnitude 6
100 x
how many times brighter is a magnitude brighter than the previous
100^1/5
2.51
are we able to observe magnitudes lower than 6 and negative magnitudes
yes
what is luminosity
the total power output of a star
measure is watts
what is apparent magnitude
apparent magnitude being measured from a distance of 10 pc
distance modulus equation
m - M = 5 log (d/10)
what is a blackbody
an idealised emitter and absorber of radiation (object that absorbs all radiation and emits radiation over a continuous range of wavelengths)
what is the area under a black body curve
total energy radiated per unit of time per unit of surface area by the object at that temperature
what do you have to remember when drawing black Body curve diagrams
The left hand side must be drawn steeper than the right hand side
The intensity must decrease towards (but not reach) zero as the wavelength increases.
The line must not cross the intensity axis (y-axis)
what is peak wavelength determined by for a black body
temperature
what is weins displacement law
λmaxT=2.9×10−3m⋅K
what is weins law used for
to find the surface temperature of the star
stefan boltzman law describes
The temperature of a blackbody and the amount of energy it radiates
what is stefan Boltzmann law
P=σAT^4
σ = 5.67×10−8Wm−2K−4
A = 4πr^2
what does energy flux or surface flux show
shows energy leaving the star
what is the energy flux or surface flux of the star
P=σT^4
what happens when photons are absorbed by electrons in a cool gas
a dark line is created in an continuous spectrum
what is the order of the hydrogen Balmer lines
O B A F G K M
what is the temperature range for O
25,000 - 50,000
what is the temperature range an the strongest absorption lines for B
11,000 - 25,000
He H
what is the temperature range an the strongest absorption lines for A
7,500 - 11,000
H
what is the temperature range an the strongest absorption lines for F
6,000-7,500
ionised metals
what is the temperature range an the strongest absorption lines for G
5000 - 6000
ionised and neutral metals
what is the temperature range an the strongest absorption lines for K
3,500 - 5,000
neutral metals
what is the temperature range an the strongest absorption lines for M
less than 3,500
neutral atoms, TiO
what is on the axis of HR diagram
spectral class or temp on the x axis
and absolute magnitude or luminosity on the y axis
where is the main sequence on the HR graph
absolute magnitude from -10 to 15
spectral classes O to M
shape squiggly line from left to right
where is super giants on the HR graph
absolute magnitude from -5 to -10
spectral classes A to end of M
shape oval
where is giants on the HR graphs
absolute magnitude of zero
spectral classes start of g to end of M
shape oval
where is white dwarfs on HR graph
absolute magnitude between 10 15
spectre class between B
shape oval
length of axis on HR diagram
-10 to 15 y axis
O to M
how are stars born
out of nebulae. the gravitational forces pull at the gas compressing it forming protostar. GPE Turns into thermal energy so interior becomes hotter and hotter. there’s fusion of hydrogen to form helium, fusion reactions cause the outer layers of protostar to become hot and a light emitting layer and protostar becomes star
what is a nebula
interstellar cloud of gas
what is a protostar
making of a star
what happens once new star is formed
star reaches internal equilibrium as inward gravitation attraction is balanced by outward radiation pressure, star becomes stable with constant luminosity.and joins the main sequence according to its mass
where does a star spend most of its time
main sequence
when does a star become a supergiant or a giant
when most of the hydrogen has been converted to helium so core collapses on itself and so outer layers of star expand and cool so star swells out and becomes super giant or giant
when does red giant become white dwarf
when nuclear fusion in the core of star stops the star cols off and the core contracts causing the outer layers to be thrown off. outer layers thrown off as shells of hot gas forming a planetary nebula
why is supernova called a supernova
because the event is brighter than a nova (new star) in the same galaxy
what is a neutron star
core of a supernova after all surrounding matter has been thrown off into space
what is a black hole
object so dense that not even light can escape it
why is a black hole so dense
because escape velocity is above the speed of light
what is the event horizon
sphere surrounding the black hole from which nothing can emerge
what is the Schwarzschild radius
radius of the event horizon
equation for Schwarzschild radius
R(s) = 2GM/c^2
